Research On The Influence Of Concealed Karst Caverns Upon The Stability Of Tunnels And Its Support Structure

Karst disaster is often encountered in tunnel construction of mountain area. The influence of concealed caverns on the stability of tunnels in Karst region is researched in this paper, which mainly contains as follows:(1) According to the survey on the tunnel Karst disaster in southwest china. Tunnel destabilization resulting from concealed Karst caverns fall into two types and the corresponding mechanics model is set up. Considering the formation of Karst caverns and the deformation property of surrounding rock, the mechanics model of Karst caverns can be divided into open-field mechanics model and excavation mechanics model according to different rheological characteristics of the surrounding mass.(2) When jumbo size concealed Karst caverns are contained, the destabilization mechanism of rock between Karst cavern and tunnel is analyzed and simplified into collapse destabilization of beams and plates. The theoretical formula for the minimal safe thickness of the tunnel roof and bedplate are deduced according to the elastic theory.(3) The most Karst tunnel problems with middle and small size caverns are mainly studied numerically with the consideration of the influence of different positions and scopes of the concealed Karst caverns on stress field, displacement field and the internal force of support structure for tunnel with the popular shape type.(4) The influence of surrounding rock conditions and the initial stresses to the displacement, stress and internal force of supporting structure of the tunnels are tested numerically.(5) A in-situ measurement for a tunnel construction in the Karst region is conducted in Wu-Dou project. The variation of tunnel displacement with and without caverns influential conditions are observed and the compared with the numerical results. The rationality and creditability of numerical conclusions are proven.